How to move an AVtransport (remove the parent from a group)

hi
I have a simple upnp app running nicely. I can remove child devices from the parent but I don't know how to solve the following scenario:

1. I play music in the Kitchen.
2. I add Bedroom to the group.
3. I remove Kitchen from the group.

I assume I should ungroup all the devices, then somehow move the AVTransport from Kitchen to Bedroom?
Just not sure how to do this using upnp

many thanks